Modulators

LFO

A two-control LFO: one knob for speed, one switch for shape. The simplest way to make a patch breathe.

What is a LFO?

Basic LFO is the simplest modulation source: a free-running low-frequency oscillator with one rate knob, one shape switch, and one bipolar output. No V/Oct, no FM, no clock sync, no reset - just speed and shape. This is the canonical "make it move" reduction: the foundation behind tremolo, vibrato, filter sweeps, and any auto-modulation. The Basic-series sibling of the full LFO, designed to teach the idea of "modulating something else" with as little surface area as possible. When you outgrow it, the full LFO adds V/Oct tracking, FM input, clock sync, reset, pulse width, offset, and invert.

In a patch

Patch OUT into a VCA CV input - your audio source now has tremolo. Patch OUT into a filter cutoff CV - your filter now sweeps automatically. Patch OUT into a VCO FM (or any pitch input) - you get vibrato. The shape switch changes the character: SIN for smooth, natural movement; TRI for similar movement with slightly brighter peaks; SAW for ramping sweeps that snap back; SQR for rhythmic on/off gating. Sweet rate: 0.05-0.2 Hz for ambient drift, 0.5-2 Hz for gentle movement, 4-8 Hz for vibrato. The output is bipolar (+/-5V) - it goes both above and below zero, so a VCA receiving this CV will go briefly silent at the LFO's low half-cycle (this is what tremolo sounds like). Need a unipolar 0-5V LFO instead? Patch through an Attenuverter with offset, or reach for the full ibp.lfo.

Outputs

OUT (cv) — Modulation output, bipolar +/-5V. Always running. Patch into any CV input that accepts bipolar signals: VCA CV (tremolo), filter cutoff CV (auto-wah / sweeps), VCO FM (vibrato), or a Scope channel to visualize the wave. Range matches Eurorack convention so it plays nicely with every CV input on the rack. The wave shape and speed are set by the SHAPE switch and RATE knob.

Controls

RATE — Speed of the LFO. Range 0.05 Hz to 20 Hz, exponential scale. 0.05 Hz gives one cycle every 20 seconds (glacial drift, ambient pad movement). 0.5-2 Hz feels like "gentle movement" - the rate at which a filter cutoff slowly opens and closes, or a tremolo wobbles. 4-8 Hz is vibrato territory - patch into a VCO FM input for a singer's vibrato. Above 12 Hz the modulation starts to feel "fluttery" rather than "moving". 20 Hz is the ceiling - the full ibp.lfo goes up to 1 kHz for very fast modulation, but Basic LFO stops here on purpose to keep the lesson on "modulation, not extra harmonics".
SHAPE — Wave shape selector. Four positions: SIN, TRI, SAW, SQR. SIN is the smooth one - natural-sounding tremolo / vibrato; the default. TRI is similar to SIN but with linear slopes and pointier peaks - slightly brighter movement. SAW is a ramp that rises slowly then snaps back to minimum - patch into filter cutoff CV for a "sweep up and reset" effect that loops on every cycle. SQR is a 50% pulse train (locked PW) that alternates between +5V and -5V - rhythmic on/off gating, useful as a CV trigger source or a "step" modulator. The label below the switch always shows which shape is currently selected.

Inspired by

A reduced LFO topology: one rate knob, one shape selector, one bipolar output. Beginners reach for it as their first modulation source - patch into a VCA CV for tremolo, a filter cutoff for sweeps, or a VCO FM input for vibrato. When they outgrow it, the full LFO adds V/Oct tracking, FM, clock-sync, reset, PW, offset, and invert.

Doepfer A-145
Behringer 110 LFO
Roland 100M (LFO section)

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